Fluid from oil wells generally includes a mixture of gas, produced water and hydrocarbon (crude oil). The real-time determination of the actual quantity of oil produced in a given well is necessary for the determination of royalties in the oil production industry. Presently, there are several methods for accomplishing such metering. As an example, the fluid stream from a well may be sent to a separation tank where it can separate by gravitational forces after which relative amounts of the various phases may be determined. However, many hours are required for this separation, and large tanks are employed. The density of heavy crude is approximately the same as that for water and separation is difficult without heating the fluid. Once heated, the densities of oil and water are sufficiently different to permit gravitational separation, but significant energy is wasted in the heating process.
Another procedure includes a phase separator, for example, a cyclone separator, for separating gas from the fluid stream. A large mechanical piping system external to the pipe carrying the mixed fluid stream is required. Once the gas is separated from the fluid, a microwave-based liquid/liquid analyzer (for example, the OW-200 series system by Agar Corporation), as an example, can be used to determine the oil-water composition. This procedure is effective for heavy crude, but in the case of light crude, more accurate density measuring devices, such as Coriolis-type meters (for example, the Coriolis meter by MicroMotion Elite) system may be used to determine the density of the oil-water mixture from which the fluid composition can be determined. Measurement systems having such capabilities are large and expensive and, as a result, it is often not possible to include such devices at every well. The flow streams from multiple wells are therefore often combined and measurements are made on the combined flow stream, which makes it difficult to determine the output of individual wells without switching the individual flow streams to the measurement device. Difficulty and expense of such measurements increases if monitoring needs to be accomplished significantly below the surface or in a deep sea operation.
If the flow stream needs to be monitored at various perforation levels in a well to determine which perforation levels are producing valuable fluids and which of the remaining levels should be closed down, a device must be lowered into the well to make this measurement. Borehole TV cameras and infra-red detectors have been used, but with limited success. Additionally, these procedures do not provide quantitative measurements of fluid composition down hole.